Recent Advances in Ambipolar Transistors for Functional Applications

Ambipolar transistors represent a class of transistors where positive (holes) and negative (electrons) charge carriers both can transport concurrently within the semiconducting channel. The basic switching states of ambipolar transistors are comprised of common offâ state and separated onâ state mainly impelled by holes or electrons. During the past years, diverse materials are synthesized and utilized for implementing ambipolar charge transport and their further emerging applications comprising ambipolar memory, synaptic, logic, and lightâ emitting transistors on account of their special bidirectional carrierâ transporting characteristic. Within this review, recent developments of ambipolar transistor field involving fundamental principles, interface modifications, selected semiconducting material systems, device structures, ambipolar characteristics, and promising applications are highlighted. The existed challenges and prospective for researching ambipolar transistors in electronics and optoelectronics are also discussed. It is expected that the review and outlook are well timed and instrumental for the rapid progress of academic sector of ambipolar transistors in lighting, display, memory, as well as neuromorphic computing for artificial intelligence.Ambipolar transistors represent transistors that allow synchronous transport of electrons and holes and their accumulation within semiconductors. This review provides a comprehensive summary of recent advances in various semiconducting materials realized in ambipolar transistors and their functional memory, synapse, logic, as well as lightâ emitting applications.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151885/1/adfm201902105_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151885/2/adfm201902105.pd

Recent advances in electronic and optoelectronic Devices Based on Two-Dimensional Transition Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides (2D TMDCs) offer several attractive features for use in next-generation electronic and optoelectronic devices. Device applications of TMDCs have gained much research interest, and significant advancement has been recorded. In this review, the overall research advancement in electronic and optoelectronic devices based on TMDCs are summarized and discussed. In particular, we focus on evaluating field effect transistors (FETs), photovoltaic cells, light-emitting diodes (LEDs), photodetectors, lasers, and integrated circuits (ICs) using TMDCs

Novel solution processable dielectrics for organic and graphene transistors

In this thesis we report the development of a range of high-performance thin-film transistors utilising different solution processable organic dielectrics grown at temperatures compatible with inexpensive substrate materials such as plastic. Firstly, we study the dielectric properties and application of a novel low-k fluoropolymer dielectric, named Hyflon AD (Solvay). The orthogonal nature of the Hyflon formulation, to most conventional organic semiconductors, allows fabrication of top-gate transistors with optimised semiconductor/dielectric interface. When used as the gate dielectric in organic transistors, this transparent and highly water-repellent polymer yields high-performance devices with excellent operating stability. In the case of top-gate organic transistors, hole and electron mobility values close to or higher than 1 cm2/Vs, are obtained. These results suggest that Hyflon AD is a promising candidate for use as dielectric in organic and potentially hybrid electronics. By taking advantage of the non-reactive nature of the Hyflon AD dielectric, the p-doping process of an organic blend semiconductor using a molybdenum based organometallic complex as the molecular dopant, has also been investigated for the first time. Although the much promising properties of Hyflon AD were demonstrated, the resulting transistors need, however, to be operated at high voltages typically in the range of 50-100 V. The latter results to a high power consumption by the discrete transistors as well as the resulting integrated circuits. Therefore, reduction in the operating voltage of these devices is crucial for the implementation of the technology in portable battery-operated devices. Our approach towards the development of low-voltage organic transistors and circuits explored in this work focused on the use of self-assembled monolayer (SAM) organics as ultra-thin gate dielectrics. Only few nanometres thick (2-5 nm), these SAM dielectrics are highly insulating and yield high geometrical capacitances in the range 0.5 - 1 μF/cm2. The latter has enabled the design and development of organic transistors with operating voltages down to a few volts. Using these SAM nanodielectrics high performance transistors with ambipolar transport characteristics have also been realised and combined to form low-voltage integrated circuits for the first time. In the final part of this thesis the potential of Hyflon AD and SAM dielectrics for application in the emerging area of graphene electronics, has been explored. To this end we have employed chemical vapour deposited (CVD) graphene layers that can be processed from solution onto the surface of the organic dielectric (Hyflon AD, SAM). By careful engineering of the graphene/dielectric interface we were able to demonstrate transistors with improved operating characteristics that include; high charge carrier mobility (~1400 cm2/Vs), hysteresis free operation, negligible unintentional doping and improved reliability as compared to bare SiO2 based devices. Importantly, the use of SAM nanodielectrics has enabled the demonstration of low voltage (<|1.5| V) graphene transistors that have been processed from solution at low temperature onto flexible plastic substrates. Graphene transistors with tuneable doping characteristics were also demonstrated by taking advantage of the SAM’s flexible chemistry and more specifically the type of the chemical SAM end-group employed. Overall, the work described in this thesis represents a significant step towards flexible carbon-based electronics where large-volume and low-temperature processing are required

Lithium-ion electrolytic substrates for sub-1V high-performance transition metal dichalcogenide transistors and amplifiers

Electrostatic gating of two-dimensional (2D) materials with ionic liquids (ILs), leading to the accumulation of high surface charge carrier densities, has been often exploited in 2D devices. However, the intrinsic liquid nature of ILs, their sensitivity to humidity, and the stress induced in frozen liquids inhibit ILs from constituting an ideal platform for electrostatic gating. Here we report a lithium-ion solid electrolyte substrate, demonstrating its application in high-performance back-gated n-type MoS2 and p-type WSe2 transistors with sub-threshold values approaching the ideal limit of 60 mV/dec and complementary inverter amplifier gain of 34, the highest among comparable amplifiers. Remarkably, these outstanding values were obtained under 1 V power supply. Microscopic studies of the transistor channel using microwave impedance microscopy reveal a homogeneous channel formation, indicative of a smooth interface between the TMD and underlying electrolytic substrate. These results establish lithium-ion substrates as a promising alternative to ILs for advanced thin-film devices

Integrated Circuits/Microchips

With the world marching inexorably towards the fourth industrial revolution (IR 4.0), one is now embracing lives with artificial intelligence (AI), the Internet of Things (IoTs), virtual reality (VR) and 5G technology. Wherever we are, whatever we are doing, there are electronic devices that we rely indispensably on. While some of these technologies, such as those fueled with smart, autonomous systems, are seemingly precocious; others have existed for quite a while. These devices range from simple home appliances, entertainment media to complex aeronautical instruments. Clearly, the daily lives of mankind today are interwoven seamlessly with electronics. Surprising as it may seem, the cornerstone that empowers these electronic devices is nothing more than a mere diminutive semiconductor cube block. More colloquially referred to as the Very-Large-Scale-Integration (VLSI) chip or an integrated circuit (IC) chip or simply a microchip, this semiconductor cube block, approximately the size of a grain of rice, is composed of millions to billions of transistors. The transistors are interconnected in such a way that allows electrical circuitries for certain applications to be realized. Some of these chips serve specific permanent applications and are known as Application Specific Integrated Circuits (ASICS); while, others are computing processors which could be programmed for diverse applications. The computer processor, together with its supporting hardware and user interfaces, is known as an embedded system.In this book, a variety of topics related to microchips are extensively illustrated. The topics encompass the physics of the microchip device, as well as its design methods and applications

Nanoscale electronic devices based on the hybrid stacks of two-dimensional materials and ferroelectric metal oxides

Further scaling of complementary metal-oxide-semiconductor (CMOS) dimensions will soon lead to a tremendous rise in power consumption while limited gain in the performance of integrated circuits. “Beyond-CMOS” devices, based on two-dimensional (2D) materials, can potentially overcome these limitations and further improve the performance, reduce energy consumption, and add novel functionalities to the CMOS platform. In this Ph.D. dissertation, we investigated energy efficient electronic devices based on a new hybrid material platform consisting of two-dimensional materials and ferroelectric metal oxides. The ferroelectric metal oxides provide programmable and non-volatile doping in the 2D materials, while the atomically thin body in 2D materials enables strong electrostatic control over the channel by the polarized ferroelectric metal oxides. We design and demonstrate a new type of classifier using ferroelectric graphene transistors, which can perform the “comparison” function in the analog domain instead of the traditional digital domain. This new type of classifier utilizes the ambipolar transport and zero bandgap of the graphene to perform the absolute difference function, |A-B|, directly. Unlike the image classifier based on silicon CMOS, the classifier based on ferroelectric graphene transistors only needs ONE transistor per pixel, which will significantly reduce chip area and energy consumption. More importantly, the embedded ferroelectric layer in the graphene transistor enables the non-volatile storage of the target image inside the analog device. Therefore, a single graphene transistor can perform both image storage and comparison functions concurrently. This in-memory computing will eliminate the need for frequent image loading/unloading, which will further reduce the power consumption related to the data transfer. We also explored non-volatile reconfigurable devices based on the hybrid stacks of ferroelectric materials and 2D materials. In traditional silicon CMOS, once the device is fabricated, its function is fixed as either an n-type or a p-type transistor. In this work, we show that functionality of this new type of device can be dynamically reconfigured during operation and the reconfiguration is non-volatile and reprogrammable. We have successfully demonstrated the electrostatic controlled reconfigurable devices based on black phosphorus and non-volatile reconfigurable devices based on molybdenum telluride and ferroelectric hafnium zirconium oxides. These reconfigurable devices will enable the logic circuits to evolve their functions on-demand. The 3D monolithic integration of these reconfigurable devices/circuits and memory blocks will enable in-memory computing and reduce the energy consumption and latency related to the transportation of “Big Data”. This work will open a new path toward the design of novel nano-function circuits based on unique material properties that are absent in traditional circuits based on CMOS logic transistors and Von Neumann architectures. These new devices will also enable a new computing paradigm, where the process latency and energy consumption will no longer be limited by the memory bottleneck

Integration of pentacene-based thin film transistors via photolithography for low and high voltage applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.An organic thin film transistor (OTFT) technology platform has been developed for flexible integrated circuits applications. OTFT performance is tuned by engineering the dielectric constant of the gate insulator and the insulator/semiconductor interface. Full integration is enabled by a low temperature photolithographic patterning process that is compatible with flexible substrates. Devices and circuits for low voltage [ ... ] and high [ ... ] voltage applications are demonstrated. Both the low and high voltage OTFTs are made from the same set of materials and processes. Low voltage operation is achieved by the use of BZN (Bi1.5Zn1Nb1.5O7) which maintains a high dielectric constant (40) at low processing temperatures. With surface treatments and back channel encapsulation for patterning, OTFTs having two distinct threshold voltages (VT > 0 V and VT 300 V) with a lower controlling voltage (VG <20 V). An offset drain/source structure enables high voltage operation. A high voltage organic thin film transistor (HVOTFT) has been fabricated. As organic semiconductors and related devices are known for their compatibility with flexible media and/or large areas, the HVOTFT would be suitable for high voltage switching on such media. Gate insulator engineering is used to tune the threshold voltage and drain current in these devices. HVOTFTs of channel length 10 [mu]m and offset length 20 [mu]m suffer from non-saturating current behavior that is similar to the short channel effects reported in short channel OTFTs and Si-based MOSFETs, and a metastable charge injection similar to that reported in a-Si based HVTFTs.by Melissa Alyson Smith.Ph.D

Low-temperature amorphous oxide semiconductors for thin-film transistors and memristors: physical insights and applications

While amorphous oxides semiconductors (AOS), namely InGaZnO (IGZO), have found market application in the display industry, their disruptive properties permit to envisage for more advanced concepts such as System-on-Panel (SoP) in which AOS devices could be used for addressing (and readout) of sensors and displays, for communication, and even for memory as oxide memristors are candidates for the next-generation memories. This work concerns the application of AOS for these applications considering the low thermal budgets (< 180 °C) required for flexible, low cost and alternative substrates. For maintaining low driving voltages, a sputtered multicomponent/multi-layered high-κ dielectric (Ta2O5+SiO2) was developed for low temperature IGZO TFTs which permitted high performance without sacrificing reliability and stability. Devices’ performance under temperature was investigated and the bias and temperature dependent mobility was modelled and included in TCAD simulation. Even for IGZO compositions yielding very high thermal activation, circuit topologies for counteracting both this and the bias stress effect were suggested. Channel length scaling of the devices was investigated, showing that operation for radio frequency identification (RFID) can be achieved without significant performance deterioration from short channel effects, which are attenuated by the high-κ dielectric, as is shown in TCAD simulation. The applicability of these devices in SoP is then exemplified by suggesting a large area flexible radiation sensing system with on-chip clock-generation, sensor matrix addressing and signal read-out, performed by the IGZO TFTs. Application for paper electronics was also shown, in which TCAD simulation was used to investigate on the unconventional floating gate structure. AOS memristors are also presented, with two distinct operation modes that could be envisaged for data storage or for synaptic applications. Employing typical TFT methodologies and materials, these are ease to integrate in oxide SoP architectures

Heterogeneous Devices and Circuits Based on 2D Semiconductors

University of Minnesota Ph.D. dissertation.September 2017. Major: Electrical/Computer Engineering. Advisor: Steven Koester. 1 computer file (PDF); xi, 123 pages.Two-dimensional (2D) semiconductors have been attracting interest for numerous device applications due to their layered crystal structure which allows great thickness scalability down to monolayer and ease of integration onto arbitrary substrates. A multitude of electronic properties of different 2D materials also enables the development of transistors with high-performance and high on/off ratio. Based on previous research, 2D materials can be used to create n-type or p-type MOS transistors without adding dopants. Thus, highly staggered gap heterostructures and integrated CMOS circuits can be realized by combining two different 2D semiconductors. Moreover, given the unique properties distinct from traditional 3D materials, the radiation effect on these materials are worth being studied in order to investigate the suitability as a counterpart of silicon in extreme conditions. In this dissertation, models, design, fabrication, and characterization of devices and circuits built with heterogeneous materials and structures are developed and presented. Firstly, a general background of 2D materials is introduced, including the history, atomic structure and fabrication technique. The miscellaneous electronic properties of materials are compared and the resulting applications are reviewed leading to the motivation of this dissertation. Secondly the local backgate structure for fabricating 2D MOSFETs is discussed including the fabrication process and the device characteristics. The device performance and radiation tolerance are shown. Thirdly, the fabrication of logic and memory circuits based on heterogeneous 2D materials is introduced, while the DC and AC measurements are reviewed. Fourthly, the MoTe2/SnSe2 heterostructure is reviewed along with the characterization of each material. A novel direct synthesized technique for lateral heterostructure is shown. Finally our work is summarized, and future developments are proposed for inspiration